Mark Zuckerberg insisted at Facebook's annual developer conference earlier this year that his company "will never be unprepared ... again" for meddling and disinformation efforts like those run by Russian trolls on its platform during the run-up to the 2016 election. Yet the social media behemoth and its competitors may still be ill-equipped for their next great challenge: Fake videos that look so real you'd believe former President Obama really did call President Trump a "dipsh*t."